My Community Forum, Helpdesk, and Knowledge Base should share the same set of Categories (or nearly the same set). Manually replicating Categories is laborious because of having to select or upload the image for each one, define the order and tree, etc..
Currently, these can't even be copied from another Forum object (like Topic Types / Status can).
Copying isn't the best method for all situations, though; so instead, there should be a Master (Project Level?) List of each of:
... that can be used across all Forum sections. And then, if desired, custom list items could be added (and/or hidden) on a Forum-by-Forum section basis.